Operation of many industrial processes requires regulation of flow of extremely fine or ultrafine powdery materials, often under circumstances that permit or tolerate only minimal leakage of the powder or any transporting gas. Where the powder is transported from a vacuum system, leakage of air or other gas by the valve destroys the vacuum and the efficiency of transport in the system. Additionally, many ultrafine particles are pyrophoric or highly combustible, so that leakage of air by the valve can result in an explosion hazard. Again, if the powder is an electrically conductive material, electric discharge on opening of certain types of valves may cause erosion of the valve seat at the least and explosion at the worst.
The regulation of transport of fine aluminum powder (e.g., 25 microns) has posed a significant problem. This material, though normally at least partially oxidized because of its pyrophoric nature, is electrically conductive and tends to stick to all valve components.
Among those valves previously employed in transport in such processes are valves referred to as flapper or clapper valves. These valves utilize a closing plate or disc anchored on and moving around a pivot, the plate being brought into sealing engagement with a seat for closing. In one valve that has seen duty in a number of industrial processes, the plate is fastened to a pivot arm by means of structure including an anchor pin. The pin fastening arrangement has proven unsatisfactory. In particular, the pin fastening arrangement permits sliding movement of the plate which results in erosion of the seat and plate seals, with consequent loss of sealing contact. Usage has also determined that the pin fastener structure also serves as a collection point for the powdery material and causes the pin to seize.
Accordingly, a need has existed for an improved valve which addresses and overcomes these problems. The invention is such a valve.